Implement verdict expression. (#7)
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Tom D
Michael Stapelberg
parent
2610769f25
commit
7612760462
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@ -0,0 +1,89 @@
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// Copyright 2018 Google LLC. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package expr
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import (
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"fmt"
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"github.com/google/nftables/binaryutil"
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"github.com/mdlayher/netlink"
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"golang.org/x/sys/unix"
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)
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// This code assembles the verdict structure, as expected by the
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// nftables netlink API.
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// For further information, consult:
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// - netfilter.h (Linux kernel)
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// - net/netfilter/nf_tables_api.c (Linux kernel)
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// - src/expr/data_reg.c (linbnftnl)
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type Verdict struct {
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Kind VerdictKind
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}
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type VerdictKind uint64
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// Verdicts, as per netfilter.h.
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const (
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VerdictDrop VerdictKind = iota
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VerdictAccept
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VerdictStolen
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VerdictQueue
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VerdictRepeat
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VerdictStop
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)
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func (e *Verdict) marshal() ([]byte, error) {
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// A verdict is a tree of netlink attributes structured as follows:
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// NFTA_LIST_ELEM | NLA_F_NESTED {
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// NFTA_EXPR_NAME { "immediate\x00" }
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// NFTA_EXPR_DATA | NLA_F_NESTED {
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// NFTA_IMMEDIATE_DREG { NFT_REG_VERDICT }
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// NFTA_IMMEDIATE_DATA | NLA_F_NESTED {
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// the verdict code
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// }
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// }
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// }
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codeData, err := netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NFTA_VERDICT_CODE, Data: binaryutil.BigEndian.PutUint32(uint32(e.Kind))},
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})
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if err != nil {
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return nil, err
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}
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immData, err := netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NLA_F_NESTED | unix.NFTA_DATA_VERDICT, Data: codeData},
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})
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if err != nil {
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return nil, err
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}
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data, err := netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NFTA_IMMEDIATE_DREG, Data: binaryutil.BigEndian.PutUint32(unix.NFT_REG_VERDICT)},
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{Type: unix.NLA_F_NESTED | unix.NFTA_IMMEDIATE_DATA, Data: immData},
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})
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if err != nil {
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return nil, err
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}
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return netlink.MarshalAttributes([]netlink.Attribute{
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{Type: unix.NFTA_EXPR_NAME, Data: []byte("immediate\x00")},
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{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: data},
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})
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}
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func (e *Verdict) unmarshal(data []byte) error {
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return fmt.Errorf("not yet implemented")
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}
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@ -731,3 +731,101 @@ func TestConfigureClamping(t *testing.T) {
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t.Fatal(err)
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}
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}
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func TestDropVerdict(t *testing.T) {
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// The want byte sequences come from stracing nft(8), e.g.:
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// strace -f -v -x -s 2048 -eraw=sendto nft add table ip nat
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//
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// The nft(8) command sequence was taken from:
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// https://wiki.nftables.org/wiki-nftables/index.php/Mangle_TCP_options
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want := [][]byte{
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// batch begin
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[]byte("\x00\x00\x00\x0a"),
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// nft flush ruleset
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[]byte("\x00\x00\x00\x00"),
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// nft add table ip filter
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[]byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x08\x00\x02\x00\x00\x00\x00\x00"),
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// nft add chain filter forward '{' type filter hook forward priority 0 \; '}'
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[]byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0c\x00\x03\x00\x66\x6f\x72\x77\x61\x72\x64\x00\x14\x00\x04\x80\x08\x00\x01\x00\x00\x00\x00\x02\x08\x00\x02\x00\x00\x00\x00\x00\x0b\x00\x07\x00\x66\x69\x6c\x74\x65\x72\x00\x00"),
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// nft add rule filter forward tcp dport 1234 drop
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[]byte("\x02\x00\x00\x00\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0c\x00\x02\x00\x66\x6f\x72\x77\x61\x72\x64\x00\xe4\x00\x04\x80\x24\x00\x01\x80\x09\x00\x01\x00\x6d\x65\x74\x61\x00\x00\x00\x00\x14\x00\x02\x80\x08\x00\x02\x00\x00\x00\x00\x10\x08\x00\x01\x00\x00\x00\x00\x01\x2c\x00\x01\x80\x08\x00\x01\x00\x63\x6d\x70\x00\x20\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x00\x0c\x00\x03\x80\x05\x00\x01\x00\x06\x00\x00\x00\x34\x00\x01\x80\x0c\x00\x01\x00\x70\x61\x79\x6c\x6f\x61\x64\x00\x24\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x02\x08\x00\x03\x00\x00\x00\x00\x02\x08\x00\x04\x00\x00\x00\x00\x02\x2c\x00\x01\x80\x08\x00\x01\x00\x63\x6d\x70\x00\x20\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x01\x08\x00\x02\x00\x00\x00\x00\x00\x0c\x00\x03\x80\x06\x00\x01\x00\x04\xd2\x00\x00\x30\x00\x01\x80\x0e\x00\x01\x00\x69\x6d\x6d\x65\x64\x69\x61\x74\x65\x00\x00\x00\x1c\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x00\x10\x00\x02\x80\x0c\x00\x02\x80\x08\x00\x01\x00\x00\x00\x00\x00"),
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// batch end
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[]byte("\x00\x00\x00\x0a"),
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}
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c := &nftables.Conn{
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TestDial: func(req []netlink.Message) ([]netlink.Message, error) {
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for idx, msg := range req {
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b, err := msg.MarshalBinary()
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if err != nil {
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t.Fatal(err)
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}
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if len(b) < 16 {
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continue
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}
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b = b[16:]
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if len(want) == 0 {
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t.Errorf("no want entry for message %d: %x", idx, b)
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continue
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}
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if got, want := b, want[0]; !bytes.Equal(got, want) {
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t.Errorf("message %d: %s", idx, linediff(nfdump(got), nfdump(want)))
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}
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want = want[1:]
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}
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return req, nil
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},
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}
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c.FlushRuleset()
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filter := c.AddTable(&nftables.Table{
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Family: nftables.TableFamilyIPv4,
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Name: "filter",
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})
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forward := c.AddChain(&nftables.Chain{
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Name: "forward",
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Table: filter,
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Type: nftables.ChainTypeFilter,
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Hooknum: nftables.ChainHookForward,
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Priority: nftables.ChainPriorityFilter,
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})
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c.AddRule(&nftables.Rule{
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Table: filter,
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Chain: forward,
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Exprs: []expr.Any{
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// [ meta load l4proto => reg 1 ]
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&expr.Meta{Key: expr.MetaKeyL4PROTO, Register: 1},
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// [ cmp eq reg 1 0x00000006 ]
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&expr.Cmp{
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Op: expr.CmpOpEq,
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Register: 1,
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Data: []byte{unix.IPPROTO_TCP},
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},
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// [ payload load 2b @ transport header + 2 => reg 1 ]
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&expr.Payload{
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DestRegister: 1,
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Base: expr.PayloadBaseTransportHeader,
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Offset: 2,
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Len: 2,
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},
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// [ cmp eq reg 1 0x0000d204 ]
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&expr.Cmp{
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Op: expr.CmpOpEq,
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Register: 1,
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Data: []byte{0x04, 0xd2},
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},
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// [ immediate reg 0 drop ]
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&expr.Verdict{
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Kind: expr.VerdictDrop,
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},
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},
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})
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if err := c.Flush(); err != nil {
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t.Fatal(err)
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}
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}
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